Since photographic light-sensitive materials generally comprise a support and photographic layers having an electric insulating property, it is likely that static electricity is accumulated in the light-sensitive materials due to contact friction between them or with other substances or by peeling during the production of the light-sensitive materials or upon use. The accumulated static charge induces many disturbances, the most serious of which is exposure of the light-sensitive emulsion layer to the electrostatic charge discharged before development processing to cause dot-like, arborescent or feathery blackening called static marks when the photographic films are developed. Such static marks significantly depress or sometimes destroy the commercial value of the photographic films. For example, static marks appearing in photographic films for medical use or in industrial X-ray films can lead to an inacurate diagnosis. This phenomenon is one of the most troublesome problems since it does not present itself until development processing. Further, the accumulated static charge causes secondary disorders, such as adhesion of dust onto the film surface, uneven coating and the like.
As described above, electrostatic charge is frequently accumulated during the production of photographic light-sensitive materials or at the time of use. For example, static electricity is generated by contact friction between photographic films and rollers during the production of the films, separation between the emulsion side and the support side during winding or rewinding of the films, and the like. It is also generated by contact or separation of X-ray films with or from machanical parts of an automatic X-ray camera or a fluorescent intensifying screen. Further, abrasion with wrapping materials also causes generation of static charge. Static marks of the photographic light-sensitive material induced by accumulation of such static charge become conspicuous with an increase of sensitivity and processing speed of the light-sensitive material. In particular, with the recent development of high sensitivity, rapid coating, high speed photography, rapid automatic processing, and the like, photographic light-sensitive materials receive severe handlings on increasing occations so that they easily undergo generation of static marks.
In order to eliminate these problems ascribed to static electricity, it is desirable to add an antistatic agent to the photographic light-sensitive material. However, antistatic agents commonly employed in other fields cannot be applied as such to photographic light-sensitive materials because of various limitations inherent to photographic light-sensitive materials. In other words, antistatic agents applicable to photographic light-sensitive materials should meet various requirements such that: photographic properties, such as sensitivity, fog, graininess, sharpness and the like is not adversely affected; film strength is not impaired, i.e., the film surface is not made susceptible to scratches; adhesion resistance of the film surface is not lessened, i.e., the adhesion of the light-sensitive materials among themselves or to other substances is not induced; fatigue of a processing solution is not accelerated; adhesion strength between layers constituting the light-sensitive materials is not reduced; and the like. Therefore, application of conventional antistatic agents to photographic light-sensitive materials have many restrictions.
Another solution to eliminate problems due to static electricity comprises increasing the electric conductivity of the surface of the light-sensitive materials so that the static charge may be scattered in a short time before the accumulated charge is discharged.
To this effect, there had been attempts at improving the conductivity supports or various coating surface layers of photographic light-sensitive materials, and the use of various hygroscopic substances or water-soluble inorganic salts, a certain kind of surface active agents, polymers, and the like has been proposed. Examples of these compounds include polymers as disclosed, e.g., in U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291, 3,615,531, 3,753,716 and 3,938,999, etc.; surface active agents as disclosed, e.g., in U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, 3,552,972 and 3,655,387, etc.; metal oxides and colloidal silica as disclosed, e.g., in U.S. Pat. Nos. 3,062,700, 3,245,833 and 3,525,621, etc.; and the like.
These numerous compounds, however, show specificity depending upon the type of supports or photographic compositions. In other words, they may afford satisfactory results to specific film supports, photographic emulsions or other photographic elements, but do not serve the purpose of preventing static charge for other supports or photographic emulsions and, in some cases, even adversely affect the photographic properties of the light-sensitive material.
Further, some of them cannot be employed because of adverse influences on the photographic properties, such as sensitivity, fog, graininess, sharpness, and the like, despite of their remarkable effect to prevent static charge. For example, polyethylene oxide type compounds are generally known to have an antistatic effect but frequently exert unfavorable influences on photographic properties, such as increase of fog, desensitization, deterioration of graininess, etc. It has been particularly difficult to establish a technique for effectively imparting antistaticity to light-sensitive materials having coated a photographic emulsion on both sides of their support, such as direct X-ray films for medical use. Thus, application of known antistatic agents to photographic light-sensitive materials is very difficult and is restricted within narrow limits.
Still another solution for overcoming problems due to static electricity comprises controlling the voltage charged on the surface of the light-sensitive material so as to lessen the generation of static electricity due to friction or contact.
To this effect, application of fluorine-containing surface active agents to photographic light-sensitive materials has been attempted as described, e.g., in British Pat. Nos. 1,330,356 and 1,524,631, U.S. Pat. Nos. 3,666,478 and 3,589,906, Japanese Patent Publication No. 26687/77, Japanese Patent Application (OPI) Nos. 46733/74 and 32322/76 (the term "OPI" herein used means "unexamined published application"), etc. However, since the static electricity characteristic of the photograhic light-sensitive materials containing these fluorine-containing surface active agents makes use of the properties of the surface active agents, such as the monomolecular layer-forming property, it is greatly dependent on the production conditions of the light-sensitive materials. Thus, it is very difficult to stably produce uniform products having constant static electricity characteristics. For example, the static electricity characteristic the products widely varies depending on the temperature and humidity during a coating step of the layers on a support, the temperature, humidity and drying time of a drying step after coating, and the like. As a result, some products have satisfactory performances while some products are considerably inferior in static electricity characteristic, thus giving rise to a serious barrier to maintenance of quality. Further, these fluorine-containing surface active agents are also disadvantageous in that even if the products have a satisfactory static electricity characteristic immediately after preparation, such a quality is gradually deteriorated with the passage of time only to exhibit no satisfactory static electricity characteristic any longer at the time of use.
In order to overcome the above-described disadvantages of the fluorine-containing surface active agents, an attempt to use a fluorine-containing polymer in the photographic light-sensitive materials, particularly in the surface layer thereof, has been made. Examples of such a polymer include an emulsion (latex) of a homopolymer of an acrylic ester or methacrylic ester of a fluorine-containing alcohol or a copolymer of said fluorine-containing monomer with other monomers as disclosed in U.S. Pat. No. 4,266,015; a copolymer comprising the above-described fluorine-containing monomer and a monomer having a polyethylene oxide chain as disclosed in U.S. Pat. No. 4,299,524; a polymer comprising the above-described fluorine-containing monomer or other fluorine-containing monomer, e.g., a vinyl ester of a fluorine-containing carboxylic acid, a fluorine-containing vinyl ether, a fluorine-substituted olefin, etc., and a monomer containing a quaternary nitrogen atom as disclosed in Japanese Patent Publication No. 15376/82 (British Pat. No. 1,535,685); a ternary copolymer comprising a melic ester of a fluorine-containing alcohol, maleic acid and another monomer as disclosed in U.S. Pat. No. 3,753,716.
When these fluorine-containing polymers are applied to photographic light-sensitive materials, the charged voltage of the surface of the materials can be controlled to some extent to thereby lessen generation of static electricity against the above-mentioned friction or contact to some extent. Further, use of these polymers can eliminate, to a certain extent, the above-described disadvantage associated with the fluorine-containing surface active agents, i.e., the great dependence of the static electricity characteristic upon production conditions and deterioration of the static electricity characteristic with the passage of time. Nevertheless, the photographic light-sensitive materials containing these fluorine-containing polymers are still insufficient in the above-described electric charging characteristic and also disadvantageous with respect to photographic properties or film properties that are important for photographic light-sensitive materials. These disadvantages significantly diminish the commercial value of products and, therefore, these polymers cannot be practically utilized for photographic light-sensitive materials.
More specifically, a photographic layer containing the emulsion of the fluorine-containing polymer as disclosed in U.S. Pat. No. 4,266,015 is highly adhesive and easily sticks to other emulsion layers or backing layers, resulting in the failure to separate from each other or appreciable traces are left after separation. In addition, the layer containing such a polymer is easily scratched by friction with other substances. These disadvantages seriously detract from the commercial value of products. On the other hand, the fluorine-containing polymers disclosed in U.S. Pat. No. 4,299,524, Japanese Patent Publication No. 15376/83 (British Pat. No. 1,535,685) and U.S. Pat. Nos. 3,753,716, when incorporated in photographic light-sensitive materials, are significantly inferior in terms of the capacity to control the charged voltage and, therefore, should be incorporated in a large quantity to compensate therefor. This not only entails an increase of cost but also adversely affects the photographic properties, resulting in reduction of sensitivity, reduction of density and generation of fog, and, further, have unfavorable influences on the film properties, such as stickiness and susceptibility to scratches. Therefore, it has been impossible to apply these polymers to photographic light-sensitive materials.
As a solution to overcome the above-described disadvantages of fluorine-containing polymers, British Pat. No. 2,080,559 and U.S. Pat. No. 4,362,812 disclose the use of fluorine-containing polymers obtained by copolymerizing a hydrophobic fluorine-containing monomer which is a styrene derivative and a water-soluble monomer.
Incorporation of these fluorine-containing polymers in photographic light-sensitive materials makes it possible to control charged voltage with reduced amounts as compared with the aforesaid fluorine-containing polymers and, therefore, succeeds to reduce the cost of the products and lessen the unfavorable influences the photographic properties, such as decrease of sensitivity and density and generation of fog, or the film properties, such as stickiness or susceptibility to scratches.
The latest developments in increase of photographic sensitivity have led to high sensitivity photographic light-sensitive materials as exemplified by negative color films or reversal color films having ISO sensitivity of 1600. The photographic properties of these high sensitivity light-sensitive materials are so sensitive that they are sometimes widely varied by incorporation of even a slight amount of a different substance. Hence, if antistatic agents are used in these high sensitivity light-sensitive materials, they are required not only to be inactive to photographic emulsions but to produce effective antistatic activity in amounts as low as possible.
The above-described fluorine-containing polymers had succeeded in the realization of sufficient static charge prevention without adversely affecting the photographic properties as far as they are used in low sensitivity photographic light-sensitive materials, but cannot be applied any longer to the recently developed high sensitivity photographic light-sensitive materials for the reasons set forth above. That is, application of these fluorine-containing polymers to high sensitivity photographic light-sensitive materials is unavoidably accompanied with adverse influences on the photographic properties, such as reduction of sensitivity, reduction of density and generation of fog. Further, the rates of development processing have recently been increased so that the photographic light-sensitive materials are to be subjected to rapid development processing under severer conditions than before. In this situation, the photographic properties also become very sensitive as in the case of achievement of high sensitivity. Accordingly, antistatic agents to be used in photographic light-sensitive materials should not only be inactive to photographic emulsions but also exert effective antistatic activity in as low amounts as possible even under the above-described severe conditions. Therefore, the above-described fluorine-containing polymers are no longer employable in photographic light-sensitive materials because the materials, having been rendered antistatic by the incorporation of such polymers, suffer from deterioration of the photographic properties when subjected to rapid development processing.
Moreover, with the recent development of the rapid coating technique in the production of photographic light-sensitive materials, a high pressure is imposed on a coated surface of the light-sensitive materials primarily in the winding step of the coated materials. Therefore, the coated surfaces of the photographic light-sensitive materials are required to have high adhesion resistance to avoid sticking to each other.
As long as the production of light-sensitive materials is performed at a conventional speed, the surface of the materials receive only a weak pressure and, therefore, the above-described fluorine-containing polymers have been employable to attain sufficient adhesion resistance. However, realization of rapid coating has made these fluorine-containing polymers unemployable due to insufficient adhesion resistance against the high pressure applied on the coated surface.
The aforesaid fluorine-containing polymers belong to the so-called random copolvmers. Random copolymers generally comprise two or more monomers aligned at random, wherein mixing of different components takes place by monomer units so that homogeneous polymer compounds can easily be obtained, while mutual interaction between components and the like frequently result in the failure to produce polymers retaining the properties of respective monomers. Blended polymers obtained by merely blending different kinds of polymers undergo phase separation due to immiscibility among the polymers in many cases. On the other hand, graft polymers comprising a polymer chain composed of a certain monomer unit to which a polymer composed of a different monomer unit is grafted are free from phase separation as encountered in the case of blended polymers, and are characterized by micro-phase separation to have a multiphase structure since the two different polymers are chemically bonded. This is a conspicuous characteristic of graft polymers that can be achieved by neither random copolymers nor blended polymers. Graft polymers are also characterized by easiness to obtain surface orientation. For example, Yamashita et al., Polymer Bulletin, Vol. 7, 289-294 (1982) evaluated the surface orientation of a fluoroalkyl acrylate by adding a graft polymer composed of a fluoroalkyl acrylate as a main chain component and methyl methacrylate as a branch component to polymethyl methacrylate and determining a contact angle with water of a surface of a film prepared therefrom. According to their evaluation, the graft polymer composed of the fluoroalkyl acrylate and methyl methacrylate brings the surface orientation of the fluoroalkyl acrylate component in an amount about 1/10 of a random copolymer composed of these two components. Thus, graft polymers absolutely differ from random copolymers as having various characterisitcs that cannot possible be attained by random copolymers.
For details of various characteristics of graft polymers, additional reference can be made to Kobunshi Kagaku Kai (ed.), Polymer Alloy, Tokyo Kagaku Dojin, R. J. Ceresa (ed.), Block and Graft Polymerization, Vol. 1, John Willey & Sons (1973), and the like.
As a result of extensive investigations to overcome the above-described disadvantages associated with the conventional fluorine-containing random copolymers, the present inventors have noted graft polymers which completely eclipsed random copolymers in various aspects as discussed above, and it has now been found that a graft polymer derived from a hydrophobic fluorine-containing monomer and a hydrophilic monomer can eliminate every disadvantage of the aforesaid fluorine-containing random copolymers when used as an antistantic agent for photographic light-sensitive materials.